At a previous job, my employer required all employees to have a page on Facebook and we were all supposed to "friend" the company's corporate page. I told them "Fire me if you like, I refuse to join Facebook." Worked there for quite a while, and never got called out on it. I did, however, have to list any on-line communities I was part of in my "Disclosure and Background Check Release" to get my security clearances. They told me I had to stop posting in the sci-fi discussion group I was a member of. While that was a small price to pay for an amazing paycheck doing something I enjoyed, I thought it was a little draconian.
With their complete dropping of the Facebook requirement, I wonder if I'd have called their bluff if they would have done anything.